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Outsourcing Computations Goal? – Outsource a computation by sending the following to a cloud A computation (e.g., a (sequence of operations)) Input data – Get back the final result data set 09/20/2011Fall 2011 Lecture 10 | UAB | Ragib Hasan3

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Map Reduce Most popular dataflow computing system Invented by Google and at one time widely used for indexing webpages and pageranks Allows large scale reliable computation 09/20/2011Fall 2011 Lecture 10 | UAB | Ragib Hasan9

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Sampling Key idea: – Feed known values in the inputs, check for known outcomes in the corresponding outputs Advantages – Efficient Disadvantages: – A clever attacker can figure out the test inputs and be honest for that cycle 09/20/2011Fall 2011 Lecture 10 | UAB | Ragib Hasan17

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Replication Key idea: – Replicate the same computation using multiple set of nodes – Use majority voting to verify correctness Advantages: – Computationally faster (same speed since all computations can run in parallel) Disadvantages: – Costly, since multiple copies of same computations need to be run – Can be defeated by a clever adversary 09/20/2011Fall 2011 Lecture 10 | UAB | Ragib Hasan18